During a pregnancy ultrasound, your doctor or sonographer may mention:
“There appears to be an accessory placental lobe.”
The ultrasound report may use the term:
Succenturiate lobe
or
Succenturiate placenta
It can sound as if there are two separate placentas.
But a succenturiate lobe usually means something more specific:
There is a smaller additional piece of placental tissue separate from the main placenta, connected by membranes and often fetal blood vessels.
Many pregnancies with an accessory placental lobe progress normally.
However, identifying it before delivery can be important because clinicians need to understand where the connecting vessels travel and make sure all placental tissue is delivered after the baby is born.
What Is a Succenturiate Placental Lobe?
Normally, the placenta forms as one main disc attached to the uterine wall.
With a succenturiate placenta, there is:
one main placental disc
plus
one or more smaller accessory lobes.
The accessory lobe is separated from the main placenta by membranes.
Blood vessels may travel through those membranes to connect the two portions.
That vascular connection is one of the most important things to evaluate on ultrasound.
Does It Mean I Have Two Placentas?
Not exactly.
A succenturiate lobe is better thought of as an additional piece of the same placenta rather than a completely independent second placenta.
For example, ultrasound might show:
main placenta → connecting vessels → accessory lobe
The accessory lobe may be much smaller than the main placental disc.
What Does It Look Like on Ultrasound?
The sonographer may notice placental tissue in an area separate from the main placenta.
It may appear similar in echogenicity and texture to the primary placenta.
When an accessory lobe is suspected, the examination may include:
- location of the main placenta
- location of the accessory lobe
- relationship to the cervix
- connecting membranes
- connecting fetal vessels
- umbilical cord insertion
- color Doppler assessment
The goal is not simply to confirm that extra placental tissue exists.
The route of the vessels can be even more important.
Why Is Color Doppler Important?
Color Doppler helps identify blood vessels running between the main placenta and accessory lobe.
This matters because some of these vessels may travel through the membranes without the protection of placental tissue or the umbilical cord.
If fetal vessels pass close to or across the internal cervical os, clinicians must evaluate for:
Vasa previa
That is a separate but very important condition.
What Is Vasa Previa?
Vasa previa occurs when unprotected fetal blood vessels run through the membranes over or very close to the cervical opening.
These vessels can be vulnerable if the membranes rupture during labor.
Succenturiate placental lobes are one recognized risk factor for vasa previa because vessels may need to travel through the membranes to connect the placental lobes.
But this distinction is essential:
Succenturiate lobe does NOT automatically mean vasa previa.
The vessels must actually be mapped.
How Does Ultrasound Check for Vasa Previa?
If an accessory lobe is identified—especially when it is near the lower uterus—the sonographer may evaluate the cervical region carefully.
Color Doppler can help determine:
Where are the connecting vessels?
Do they approach the internal cervical os?
Do any vessels cross the os?
Transvaginal ultrasound with color Doppler may be used when a more accurate assessment of the cervical region is needed.
This examination can be extremely important for delivery planning.
Is Transvaginal Ultrasound Safe?
Yes.
When clinically indicated, transvaginal ultrasound provides a detailed view of the cervix and nearby vessels.
The probe remains within the vagina.
It does not enter the uterus or touch the placenta or baby.
When evaluating possible vasa previa, the combination of transvaginal ultrasound and color Doppler can provide valuable information about vessel location.
Does an Accessory Placental Lobe Hurt the Baby?
Usually, the presence of the extra lobe itself does not directly harm the fetus.
Many babies with a succenturiate placenta grow normally.
The main concerns are generally related to:
connecting fetal vessels
and
retained placental tissue after delivery.
So the finding is less about:
“Is the extra placenta dangerous?”
and more about:
“Where are the vessels, and will the entire placenta be delivered?”
Does It Cause Fetal Growth Restriction?
An accessory lobe alone does not automatically mean the placenta cannot support normal fetal growth.
Fetal growth should still be interpreted within the overall pregnancy.
If there are additional placental abnormalities or growth concerns, your healthcare provider may recommend follow-up ultrasound.
But:
Succenturiate lobe ≠ automatic placental insufficiency.
Why Does the Location Matter?
Imagine the main placenta is on the posterior uterine wall while a smaller accessory lobe lies anteriorly.
Connecting vessels may travel between them through the membranes.
If those vessels are far away from the cervix, the situation may be relatively straightforward.
But if the accessory lobe and main placenta are positioned so that the connecting vessels travel across the lower uterine segment, clinicians need to determine whether they approach the cervical opening.
That is why ultrasound should evaluate the entire placental arrangement, not just each lobe separately.
Is It the Same as a Bilobed Placenta?
Not exactly.
The terms can sometimes be confused.
Succenturiate placenta
There is a main placental disc with a smaller accessory lobe.
Bilobed placenta
The placenta is divided into two more similarly sized lobes.
Both conditions can have vessels running through membranes between placental tissue.
Therefore, in either situation, the location of connecting vessels may be important.
Is It the Same as Placenta Previa?
No.
Placenta previa describes placental tissue covering the internal cervical os.
Succenturiate placenta describes placental shape and the presence of an accessory lobe.
However, the accessory lobe itself could theoretically be located low in the uterus.
Therefore, clinicians evaluate both:
placental tissue location
and
connecting vessel location.
Is It the Same as Placenta Accreta?
No.
Placenta accreta spectrum involves abnormal attachment of placental tissue to the uterine wall.
A succenturiate lobe simply means there is an additional placental lobe.
They are separate conditions.
A person can have an accessory lobe without placenta accreta.
Why Is It Important After Delivery?
This is one of the most practical reasons to identify an accessory lobe before birth.
After the baby is delivered, the placenta must also be delivered.
If the main placental disc separates but the accessory lobe remains attached inside the uterus, this can result in:
retained placental tissue.
Retained placental tissue may contribute to:
postpartum bleeding
or
postpartum infection.
Knowing about the accessory lobe beforehand helps the delivery team inspect the placenta carefully and confirm that all lobes appear to have been delivered.
Does It Mean I Will Have Postpartum Hemorrhage?
Not automatically.
A succenturiate lobe is associated with a risk of retained placental tissue, and retained tissue can contribute to postpartum hemorrhage.
But identifying an accessory lobe does not mean hemorrhage will occur.
It means the delivery team should be aware of the placental anatomy.
This is a good example of how a prenatal ultrasound finding can be useful even when the baby itself is completely healthy.
Will I Need More Ultrasounds?
Possibly.
Follow-up may be recommended depending on:
- location of the accessory lobe
- location of connecting vessels
- proximity to the cervix
- concern for vasa previa
- fetal growth
- other placental findings
If the connecting vessels are clearly far from the cervix and the rest of the pregnancy is reassuring, management may be relatively routine.
Does It Mean I Need a C-Section?
Not simply because an accessory lobe exists.
If there is no vasa previa and no other obstetric indication for cesarean delivery, the accessory lobe itself does not automatically require a C-section.
However, if vasa previa is confirmed, delivery planning changes significantly because protecting those fetal vessels becomes critical.
So again, the determining issue is not merely the extra placental tissue.
It is:
Where do the vessels run?
Can the Accessory Lobe Disappear?
Placental tissue does not usually simply disappear.
However, visualization can change as the uterus grows and fetal position changes.
An accessory lobe that was difficult to see on one examination may become easier—or harder—to visualize later.
This is why documenting its location and vascular connections when clearly seen can be useful.
Did I Cause It?
No.
You did not cause an accessory placental lobe by:
exercise
diet
sleeping position
working
or
stress.
It develops as part of placental formation.
There is no exercise, food, or supplement that can merge the accessory lobe back into the main placenta.
Questions to Ask Your Doctor
If a succenturiate lobe is identified, useful questions include:
- Where is the main placenta?
- Where is the accessory lobe?
- How large is it?
- Can you see vessels connecting the two?
- Where do those vessels travel?
- Are any vessels near the cervix?
- Has vasa previa been excluded?
- Do I need transvaginal ultrasound with color Doppler?
- Is fetal growth normal?
- Will I need another ultrasound?
- Does this change my delivery plan?
- Will the delivery team know to check for the accessory lobe after birth?
And perhaps the most important question is:
“Are the connecting vessels safely away from the cervix?”
Key Takeaway
A succenturiate placental lobe is a smaller accessory piece of placental tissue located separately from the main placenta.
Many pregnancies with this finding progress normally.
But identifying it matters for two important reasons:
1. Connecting fetal vessels should be mapped.
This helps determine whether vasa previa is present.
2. The entire placenta should be accounted for after delivery.
This reduces the chance that an accessory lobe will remain inside the uterus unnoticed.
So when an ultrasound finds an accessory placental lobe, don’t focus only on:
“Why do I have extra placenta?”
The more useful question is:
“Where are the vessels connecting it to the main placenta?”
That is often the most important piece of the ultrasound assessment. 🩷👶
About the Author
This article was written by a sonographer with over 20 years of hands-on clinical ultrasound experience, including fetal, breast, and thyroid imaging.
When an accessory placental lobe is seen, I don’t think the most important image is simply the extra piece of placenta. What matters is tracing the relationship between the main placenta, accessory lobe, connecting vessels, and cervix. Color Doppler can make that anatomical relationship much easier to understand.
This article is for general educational purposes and does not replace individualized prenatal diagnosis, obstetric or maternal-fetal medicine evaluation, or medical advice from your healthcare provider
